Role of the nonionic surfactant Triton X-405 in emulsion polymerization. II. Homopolymerization ofn-butyl acrylate

Abstract

In the emulsion polymerization of n-butyl acrylate, the nonionic surfactant Triton X-405 (octylphenoxy polyethoxy ethanol) partitions primarily into the aqueous phase leading to nucleation in the presence of micelles and unimodal final latex particle size distributions. Nucleation is accompanied by limited aggregation in the early stages of the reactions with particles being formed in some cases past 50% conversion depending on the experimental conditions. High values of the average number of radicals per particle (n > 10) are observed during these reactions which explains a secondary increase in the heat of reaction. This increase was not observed when the initiator (K2S2O8) concentration was reduced from 6.4 to 0.6 mM or the temperature was decreased from 70°C to 60°C; contrary to what was expected, an inverse relationship was observed between the rate of polymerization and the final number of particles for these experiments. This was attributed to more extensive limited aggregation at the higher temperature and initiator concentration. Limited aggregation is thus shown to be an important mechanism in these polymerizations. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3827–3835, 1997